Product packagings having reclosure mechanisms are often employed for packaging products in situations where the consumer may wish to remove only a portion of the product and to reclose the package. Particularly with the current popularity of "fat-free" baked goods, which readily dry out if left exposed to atmosphere, there is a significant interest on the part of the product manufacturers in easily and inexpensively produced packaging which can be repeatedly opened and reclosed. Flexible packaging produced from flexible sheet materials are generally favored for reasons of cost, functionality, and marketing appeal.
Various types of reclosure mechanisms have been developed for reclosing a flexible package to keep unused portions of a food product fresh. Many of these mechanisms are separately manufactured articles which are added to the package either in a subsequent manufacturing step or by the consumer, such as zippers, reclosure tapes or tabs, seal strips, clips, and the like. However, such mechanisms are disadvantageous because they necessitate additional manufacturing operations and materials, thus increasing manufacturing cost. Accordingly, efforts have been made toward developing adhesive-based reclosure mechanisms for flexible packages, since such packaging is readily produced on automated flexible web-handling machinery, and the only component required is the flexible web to which adhesive has already been applied during the manufacturing process for the web.
The challenge in making a reclosure mechanism which relies on adhesive for resealing is that an adhesive which may be suitable for forming the original package seal, which must have sufficient strength and integrity to prevent inadvertent opening of the package and to keep the product fresh during handling and shipment, is generally different from the type of adhesive which is desirable from a resealing point of view. Cold seals, hot-melts, and heat seals provide good seal strength and are thus suitable for forming original package seals. Unfortunately, such materials do not generally provide sufficient reclosure capabilities. Pressure-sensitive adhesives can be repeatedly removed and reattached to suitable substrates and thus provide reclosure capabilities. However, pressure-sensitive adhesives do not provide sufficient closure strength to form reliable original package seals in many applications. Furthermore, because pressure-sensitive adhesives are inherently tacky and will stick to almost any surface they come in contact with, automated handling of sheets or webs to which pressure-sensitive adhesives have been applied is difficult. For example, the pressure-sensitive adhesive may become stuck to the rollers of an apparatus, a problem known in the industry as "picking." Additionally, the web may stick to itself when it is wound into a roll and stored prior to being used, a problem known as "blocking."
Accordingly, pressure-sensitive adhesives are commonly used in conjunction with backing layers of paper or other material to which a release coating has been applied, as shown in U.S. Pat. No. 3,827,625. When it is desired to operate a seal employing such a pressure-sensitive adhesive mechanism, the backing layer is removed to expose the pressure-sensitive adhesive, and the pressure-sensitive adhesive is pressed against a cooperating part of the package to effect a closure, whether an original seal or a reclosure of a previously opened seal. Alternatively, the backing layer is permanently attached to the cooperating part of the package to effect an original seal, and the substrate which carries the pressure-sensitive adhesive is peeled from the backing layer to open the original seal, as shown in U.S. Pat. No. 3,272,422. In either case, reclosure is effected by pressing the pressure-sensitive adhesive against the cooperating part or the backing layer.
The disadvantages of such closure mechanisms are that additional material and manufacturing operations are required to form the backing layer, and the strength of the original seal is only as good as the strength of the pressure-sensitive adhesive, which as previously noted is insufficient in many cases.